Typically, a wireless communication system has been developed to provide voice services while ensuring the mobility of users. However, the wireless communication system has been expanded from the voice service to a data service. In recent years, the wireless communication system has been developed to provide a high-speed data service. However, currently, the wireless communication system that provides services suffers from a lack of resources, and users require the wireless communication system to provide higher-speed services to them. Accordingly, there is a necessity for more advanced wireless communication systems.
In the same way, an average amount of data used by wireless communication users is geometrically increasing due to use of wireless mobile stations such as smart phones. In addition to that, users' demands for a higher data transmission rate have been continuously increased.
A method of providing a generally high data transmission rate includes a method of providing communication using a wider frequency band and a method of increasing frequency usage efficiency.
However, it is very difficult to provide a higher average data rate through the latter method. This is because communication technologies of a current generation provide frequency usage efficiency close to a theoretical limit and thus, it is very difficult to increase the frequency usage efficiency up to that or more through a technical improvement.
Accordingly, it can be said that a feasible method for increasing the data transmission rate is a method of providing data services through the wider frequency band. At this time, the thing to consider is an available frequency band. In view of the current frequency distribution policy, a band in which a broadband communication of 1 GHz or more is possible is limited and a practically selectable frequency band is only the millimeter wave band of 30 GHz or more.
Such a signal of the high frequency band causes severe signal attenuation according to a distance differently from a signal of a frequency band of 2 GHz used by the conventional cellular systems. Due to such signal attenuation, service providing coverage of a base station using the same power as the conventional cellular systems will be considerably reduced. In order to solve this problem, a beam forming technique is widely used which concentrates transmission/reception power into a narrow space to increase transmission/reception efficiency of an antenna.
Meanwhile, a wireless communication system may employ a Discontinuous Reception (DRX) operation to efficiently use electric power of a mobile station. A mobile station operated in the DRX may be operated largely in a normal mode and a DRX mode, and the mobile station may enter into a DRX mode if there are no data which is sent or received by the mobile station for a specific time.
However, a DRX operation of the mobile station considering the beam forming has not been defined, and a study on the DRX operation is necessary.